JP2013112888A - Method for producing composition for injection molding and composition for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for injection molding capable of obtaining a composition for injection molding in which an inorganic powder and a binder are less unevenly distributed, and as a result, capable of producing a sintered compact which is less deformed, chipped, or the like and which has high quality; and to provide a method for producing such a composition for injection molding.SOLUTION: The method for producing a composition for injection molding which contains an inorganic powder, and a binder containing a first resin and a second resin, the content of the second resin being smaller than that of the first resin, includes: a first grinding step of cryogenically grinding the first resin containing a polyacetal-based resin as a main component; a second grinding step of cryogenically grinding a second resin containing a glycidyl group-containing polymer as a main component; a mixing step of mixing the powder obtained in each step, and the inorganic powder, thereby obtaining a mixed powder; and a kneading step of kneading the mixed powder, thereby obtaining a kneaded material 1. The kneaded material 1 includes: an inner layer 21 formed so as to cover particles 2 of the inorganic powder, and containing mainly the glycidyl group-containing polymer; and an outer layer 22 located outside the inner layer, and containing mainly the polyacetal-based resin.

Description

  The present invention relates to a method for producing an injection molding composition and an injection molding composition.

The powder metallurgy method for producing a metal product by sintering a compact including a metal powder has been widely used in many industrial fields in recent years because a near-net-shaped sintered body can be obtained. Also, ceramic powder is used instead of metal powder.
There are many methods for manufacturing a molded body (molding method), and a powder injection molding method is known in which an inorganic powder and an organic binder are mixed and kneaded, and injection molding is performed using the kneaded product (compound). Yes. Thereafter, the molded body produced by the powder injection molding method is baked after the organic binder is removed by degreasing treatment, thereby obtaining a metal product and a ceramic product having a desired shape.
In such a powder injection molding method, first, a metal powder and an organic binder are kneaded to obtain a kneaded product (see, for example, Patent Document 1). Then, the obtained kneaded material is injection-molded, and the obtained molded body is degreased and fired to obtain a sintered body.

However, when the particle size of the organic binder powder is larger than the particle size of the metal powder, it takes a considerable time to mix these powders uniformly, and the temperature of the kneaded product increases with self-heating. The heat causes decomposition of the organic binder. And an organic binder will impair the original function.
Moreover, since the property of the resin material used as the organic binder is greatly different from that of the metal powder, it is easy to separate and the resin material and the metal powder are likely to be unevenly distributed. For this reason, even when the obtained injection molding composition is molded to obtain a molded body, there are problems in shape retention, such as low dimensional accuracy.

Japanese Patent Laid-Open No. 11-131103

  The object of the present invention is to obtain an injection molding composition with less uneven distribution of inorganic powder and binder, and as a result, an injection molding composition capable of producing a high-quality sintered body with few deformations and defects, And providing a method for producing such an injection molding composition.

The above object is achieved by the present invention described below.
The method for producing an injection molding composition of the present invention comprises an inorganic powder composed of at least one of a metal material and a ceramic material, and a binder containing a polyacetal resin and a glycidyl group-containing polymer. A method of manufacturing a product,
A first pulverization step of freeze-pulverizing the first resin mainly composed of the polyacetal resin;
A second pulverization step of freeze pulverizing the second resin mainly composed of the glycidyl group-containing polymer;
A mixing step of mixing the powder obtained in the first crushing step, the powder obtained in the second crushing step, and the inorganic powder to obtain a mixed powder;
A kneading step of kneading the mixed powder.
As a result, an injection molding composition with less uneven distribution of inorganic powder and binder can be obtained, and as a result, an injection molding composition capable of producing a high-quality sintered body with less deformation and defects can be efficiently produced. can do.

In the method for producing an injection molding composition of the present invention, the melting point of the glycidyl group-containing polymer is lower than that of the polyacetal resin, and the mass content of the glycidyl group-containing polymer in the injection molding composition is It is preferably less than the mass content of the polyacetal resin.
As a result, the second resin melts and flows before the first resin during kneading, so the second resin is present so as to cover the particles of the inorganic powder, and further the first resin is covered so as to cover the outside. Therefore, a significant decomposition of the first resin is suppressed, and an injection molding composition capable of forming a molded article having high shape retention is obtained.

In the method for producing an injection molding composition of the present invention, in the kneading step, the mixed powder is preferably kneaded at a temperature between the melting point of the first resin and the melting point of the second resin.
As a result, only the second resin is melted as the temperature rises during kneading, and is easily infiltrated between the inorganic powder particles and the first resin. As a result, shape retention and moldability can be highly compatible.

In the method for producing an injection molding composition of the present invention, the second resin is preferably an unsaturated glycidyl group-containing polymer.
Thereby, since inorganic powder and 2nd resin show high adhesiveness, the remarkable decomposition | disassembly of 1st resin can be suppressed more reliably.
In the method for producing an injection molding composition of the present invention, the unsaturated glycidyl group-containing polymer preferably has a melting point of 65 ° C or higher and 105 ° C or lower.
Thereby, only the second resin is reliably melted as the temperature rises at the time of kneading, and it becomes easy to penetrate between the particles of the inorganic powder and the first resin.

In the method for producing an injection molding composition of the present invention, the unsaturated glycidyl group-containing polymer is preferably a copolymer containing an unsaturated glycidyl group-containing monomer and an ethylenically unsaturated ester compound monomer. .
Thereby, the second resin functions reliably as a partition wall that separates the particles of the inorganic powder and the first resin. As a result, it is possible to suppress a decrease in shape retention of the molded body.

In the method for producing an injection molding composition of the present invention, the unsaturated glycidyl group-containing polymer is preferably a copolymer containing an unsaturated glycidyl group-containing monomer and a nonpolar α-olefin monomer. .
Thereby, the second resin can exist stably between the particles of the inorganic powder and the first resin. As a result, it is possible to particularly suppress a decrease in shape retention of the molded body.

In the method for producing an injection molding composition of the present invention, the average particle size of the binder powder is preferably 2 to 50 times the average particle size of the inorganic powder.
Thereby, the mass of each particle | grain of inorganic powder and binder powder becomes close, and more uniform mixing is attained.
The composition for injection molding of the present invention is produced by the method for producing the composition for injection molding of the present invention, is provided so as to cover the particles of the inorganic powder, and is mainly composed of the second resin. And an outer layer that is located outside the inner layer and is mainly composed of the first resin.
Thereby, the composition for injection molding which can manufacture a high quality sintered compact with few deformation | transformation, a defect | deletion, etc. is obtained.

It is sectional drawing which shows typically the structure before kneading | mixing of the composition for injection molding of this invention. It is sectional drawing which shows typically the structure (after kneading | mixing) of the composition for injection molding of this invention. It is an observation image of the composition for injection molding (kneaded material) obtained in Example 4 and Comparative Example 2.

Hereinafter, the manufacturing method of the composition for injection molding of this invention and the composition for injection molding are demonstrated in detail based on suitable embodiment shown to an accompanying drawing.
<Method for producing injection molding composition>
The manufacturing method of the composition for injection molding of this invention is a method of manufacturing the composition with which it uses for injection molding, and the manufactured composition contains an inorganic powder and a binder.
Of these, the inorganic powder is composed of at least one of a metal material and a ceramic material.

On the other hand, the binder contains a first resin mainly composed of a polyacetal-based resin, and a second resin having a smaller content than the first resin and mainly composed of a glycidyl group-containing polymer. is there.
Since the composition for injection molding produced according to the present invention is uniform and has high shape retention, it is possible to produce a high-quality sintered body with less deformation and defects.
The manufacturing method of the composition for injection molding according to the present embodiment includes a first pulverization step in which a first resin is freeze pulverized to obtain a first powder, and a second resin is freeze pulverized to produce a second powder. A second pulverizing step for obtaining a mixed powder, a mixing step for mixing the first powder, the second powder, and an inorganic powder to obtain a mixed powder, and a kneading step for kneading the mixed powder. Hereinafter, each process will be described sequentially.

[1] Grinding process First, an inorganic powder and a binder used for producing an injection molding composition are prepared.
As described above, as the inorganic powder, a powder composed of at least one of a metal material and a ceramic material is used. Specifically, in addition to metal powder and ceramic powder, powder of composite material of metal material and ceramic material, mixed powder of metal powder and ceramic powder, and the like can be mentioned.

On the other hand, the binder used in the present invention contains the first resin and the second resin having a smaller content rate.
These inorganic powder and binder will be described in detail later.
Next, each of the first resin and the second resin is freeze-ground. Thereby, the 1st powder and the 2nd powder are obtained (the 1st crushing process and the 2nd crushing process). Here, the freeze pulverization of the first resin will be described as a representative.

  Freeze crushing is a method for finely and uniformly crushing using brittleness caused by freezing a sample. A freeze pulverizer is used for the freeze pulverization. The freeze pulverizer includes a pulverization container for containing a sample and a steel ball that reciprocates in the pulverization container. The steel ball is reciprocated while cooling the pulverization container with a coolant such as liquid nitrogen. Crush the sample in the crushing container. As the sample becomes brittle with cooling, the sample having flexibility can be pulverized. The above-described freeze pulverizer is merely an example, and freeze pulverizers having other structures can also be used.

  By freeze pulverizing the first resin, it can be finely and uniformly pulverized without modifying the first resin. When a pulverization method other than freeze pulverization was used, the first resin generated heat along with the pulverization, and it was inevitable that it was denatured, melted (softened) and decomposed by heat. Melting and decomposition can be prevented. As a result, the first resin is subjected to the subsequent process while maintaining its original characteristics, and a reduction in shape retention in the molded body is prevented. Finally, it is possible to manufacture a high-quality sintered body with few deformations and defects.

  When freeze-pulverized, the obtained powder is fine, has a large specific surface area, and has high activity because denaturation is suppressed. Such a powder has high affinity for the inorganic powder, and contributes to suppression of problems such as uneven distribution when the binder powder and the inorganic powder are mixed. Therefore, freeze-grinding makes it possible to produce a particularly uniform injection molding composition.

In addition to liquid nitrogen as described above, liquid air, liquid oxygen, dry ice, or the like may be used as a coolant in freeze pulverization.
Similarly, the second resin can be freeze-ground.
The average particle sizes of the first powder and the second powder thus obtained are each preferably about 10 μm to 500 μm, and more preferably about 15 μm to 400 μm. By pulverizing to such a particle size by freeze pulverization, the first powder and the second powder can be mixed uniformly. In addition, by making the particle size after freeze pulverization within the above range, when mixing these powder and metal powder in the mixing step described later, the influence of the difference in specific gravity in mixing can be minimized. Therefore, even when the binder powder and the metal powder are mixed, they can be mixed uniformly.

Further, the average particle diameter is obtained as a particle diameter when the cumulative amount reaches 50% on a volume basis by a laser diffraction method.
Furthermore, the binder components other than the first resin and the second resin are preferably freeze-ground, but may be pulverized by other pulverization methods.
A binder powder is obtained as described above.

[2] Mixing step Next, the inorganic powder and the binder powder are mixed. This gives a mixture.
For mixing, for example, various mixers such as a stirring mixer, a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, and a ball mill are used.
Since the binder powder containing the first powder obtained by freeze pulverization has a characteristic of being uniformly mixed with the inorganic powder as described above, it is uniform in this step without causing uneven distribution. A mixture can be obtained.

Moreover, although a dry method or a wet method may be sufficient as mixing, it mixes, cooling as needed.
The sample temperature during mixing is preferably not higher than the melting point of the binder powder. Thereby, binder powder can maintain the shape of particle | grains, and it can mix uniformly using this being easy to roll. In addition, when there is no melting | fusing point, it is preferable that it is below a softening point.
The volume ratio of the binder powder to the inorganic powder is preferably 0.2 or more and 0.6 or less, and more preferably 0.3 or more and 0.5 or less. Thereby, the improvement of a moldability and shape retention property and the improvement of a sintered density can be made compatible.

The average particle size of the binder powder is preferably 2 to 50 times the average particle size of the inorganic powder, and more preferably 3 to 10 times. By satisfy | filling the said relationship about the average particle diameter of inorganic powder and binder powder, the mass of each particle | grain of inorganic powder and binder powder becomes close, and more uniform mixing is attained.
Further, the average particle size of the first powder is preferably 3 to 20 times the average particle size of the inorganic powder, and more preferably 7 to 15 times. On the other hand, the average particle size of the second powder is preferably 3 to 50 times the average particle size of the inorganic powder, and more preferably 5 to 30 times. Thereby, binder powder and inorganic powder can be mixed more uniformly.
Furthermore, the average particle size of the second powder is preferably 2 to 15 times the average particle size of the first powder, more preferably 3 to 10 times. Thereby, a 1st powder and a 2nd powder can be mixed more uniformly.

[3] Kneading step Next, the obtained mixture is kneaded. Thereby, a kneaded material, that is, an injection molding composition of the present invention is obtained.
For the kneading, for example, various kneaders such as a pressure or double-arm kneader kneader, a roll kneader, a Banbury kneader, a uniaxial or biaxial extruder are used.
Moreover, you may make it add additives, such as an organic solvent, to a mixture as needed at the time of kneading | mixing.

  Here, as the first resin, a resin mainly composed of a polyacetal resin is used, and as the second resin, a resin mainly composed of a glycidyl group-containing polymer is used. In the first resin, the component other than the main component may be a glycidyl group-containing polymer, and may be a lubricant or other components described later. Similarly, the component other than the main component in the second resin may be a polyacetal resin, and may be a lubricant or other components described later.

  By the way, as the glycidyl group-containing polymer, those having a melting point lower than that of the polyacetal resin are preferably used. Thus, when there is a difference in melting point between the glycidyl group-containing polymer and the polyacetal resin, the glycidyl group-containing polymer melts before the polyacetal resin when the temperature of the mixture rises with kneading. And flow. As a result, the fluid of the glycidyl group-containing polymer penetrates so as to cover the particles of the inorganic powder. In addition, since the polyacetal resin is a resin having relatively high rigidity, a gap is easily formed between the polyacetal resin and the inorganic powder, and the penetration of the glycidyl group-containing polymer is promoted. As a result, in the kneaded product obtained in this step, the glycidyl group-containing polymer is present so as to cover the particles of the inorganic powder, and the polyacetal-based resin is present so as to cover the outside thereof.

FIG. 1 is a sectional view schematically showing the structure before kneading of the injection molding composition of the present invention, and FIG. 2 is a sectional view schematically showing the structure (after kneading) of the injection molding composition of the present invention. It is.
In the mixture before kneading, as shown in FIG. 1, a plurality of inorganic powder particles 2 are dispersed in a binder 3. In the binder 3, a polyacetal resin, a glycidyl group-containing polymer and the like are mixed.

When such a mixture is kneaded, the temperature of the mixture rises because it is heated from the outside or self-heats with the kneading. As a result, in the obtained kneaded material 1, as shown in FIG. 2, an inner layer 21 mainly composed of a glycidyl group-containing polymer is formed so as to cover the particles 2, and a polyacetal-based resin is formed on the outer side thereof. The outer layer 22 is located.
Here, the polyacetal resin, which is the main component of the first resin, has a relatively high rigidity, so it has been used as a binder component for a long time, but it decomposes during kneading and decreases shape retention during degreasing. There was a problem to do.

In response to this problem, the inventor has intensively studied the cause of the decrease in shape retention when a polyacetal resin is used as a binder component. And it discovered that the metal element in inorganic powder was carrying out the catalytic function which accelerates | stimulates decomposition | disassembly of polyacetal type resin.
Therefore, in the present invention, together with the polyacetal resin, a glycidyl group-containing polymer having a lower melting point is used in combination, thereby suppressing the degradation of the polyacetal resin and suppressing the decrease in shape retention. That is, when the inner layer 21 is formed as described above, the inner layer 21 serves as a partition, preventing contact between the metal element in the particle 2 and the outer layer 22, thereby suppressing the catalytic action described above. As a result, sudden decomposition of the binder 3 is suppressed, and a decrease in shape retention can be avoided. In other words, the presence of the inner layer 21 makes it easier to maintain the shape of the molded body because the outer layer 22 is gradually decomposed rather than suddenly when the molded body is subjected to a degreasing treatment.

  In order to obtain such an effect, it is necessary that the polyacetal resin and the glycidyl group-containing polymer behave as described above in the binder, and in order for this behavior to occur, the polyacetal resin and the glycidyl group-containing polymer Is uniformly mixed. In the present invention, as described above, the first resin containing the polyacetal-based resin and the second resin containing the glycidyl group-containing polymer are preliminarily freeze-ground so that the first powder having a fine and high activity and The second powder can be produced, and the polyacetal resin and the glycidyl group-containing polymer can be mixed extremely uniformly. As a result, the effects of the present invention described above can be achieved.

  The kneading temperature in this step is preferably set according to the melting points of the polyacetal resin and the glycidyl group-containing polymer. Specifically, since the glycidyl group-containing polymer has a lower melting point than the polyacetal resin, the initial kneading temperature is set to a temperature between the melting point of the glycidyl group-containing polymer and the melting point of the polyacetal resin. Is preferred. By kneading at such a temperature, only the glycidyl group-containing polymer melts as the temperature rises during the kneading, and easily penetrates between the particles 2 and the polyacetal resin. As a result, the inner layer 21 and the outer layer 22 are formed, and shape retention and moldability can be highly compatible.

When the melting point of the polyacetal-based resin is T _A [° C.] and the melting point of the glycidyl group-containing polymer is T _B [° C.], the kneading temperature is T _B + 5 ° C. or more and T _A −5 ° C. or less. More preferred. By kneading at such a temperature, the above-described effects become more remarkable. Such a kneading temperature is preferably maintained for about 5 minutes or more and 180 minutes or less.
Meanwhile, after the kneading was finished under the above conditions, and ultimately may be carried out kneading at a high temperature side than the melting point T _A of the polyacetal resin. Thereby, the polyacetal resin is also melted, and the fluidity of the entire kneaded product is further improved. In this case, the final kneading temperature is preferably T _A ° C or higher and T _A + 70 ° C. or lower.
The total kneading time is preferably about 15 minutes to 210 minutes.

  The viscosity of the obtained kneaded material is preferably 500 P or more and 7000 P or less (50 Pa · s or more and 700 Pa · s or less), and more preferably 1000 P or more and 6000 P or less (100 Pa · s or more and 600 Pa · s or less). Thereby, the moldability at the time of shaping | molding can be improved especially. The viscosity is measured by a capillograph while keeping the kneaded product at a temperature of 190 ° C.

  Moreover, when a lubricant is contained in the binder 3, the lubricant is first melted to form a base for the glycidyl group-containing polymer to penetrate as described above. That is, the lubricant forms the innermost layer inside the inner layer 21. This innermost layer is considered to suppress the flow resistance of the surface of the particle 2 and promote the penetration of the glycidyl group-containing polymer. For this reason, the inner layer 21 is reliably formed in a shorter time.

  The lubricant is preferably added in an amount smaller than that of the polyacetal resin or the glycidyl group-containing polymer. Thereby, the fluidity | liquidity of a polyacetal type resin or a glycidyl group containing polymer can be improved, without inhibiting the characteristic of a polyacetal type resin or a glycidyl group containing polymer. As a result, the inner layer 21 mainly composed of the glycidyl group-containing polymer is more quickly and reliably formed, and more excellent fluidity is imparted to the outer layer 22 mainly composed of the polyacetal resin. As a result, shape retention and moldability can be achieved at a higher level.

  The thickness of the inner layer 21 is not particularly limited as long as it covers the surface of the particle 2, but for example, the average thickness is preferably 1 nm or more and 2000 nm or less, and more preferably 2 nm or more and 1000 nm or less. Thereby, shape retention property and moldability (shape transfer property) can be highly compatible. When the average thickness of the inner layer 21 is less than the lower limit value, the inner layer 21 is likely to be interrupted, so that the particles 2 and the outer layer 22 may be in contact with each other. Since the ratio of 22 falls, there exists a possibility that a moldability may fall.

Further, the outer layer 22 may not be layered as long as it is located outside the inner layer 21, and the particles 2 in the kneaded product 1 are connected to each other as shown in FIG. It may be in the form of a matrix (matrix) that disperses.
The inner layer 21 is preferably mainly composed of a glycidyl group-containing polymer, but may contain a polyacetal resin, a lubricant, and other components. Similarly, the outer layer 22 is preferably mainly composed of a polyacetal resin, but may contain a glycidyl group-containing polymer, a lubricant, and other components, and the innermost layer is mainly composed of a lubricant. However, it may contain a polyacetal resin, a glycidyl group-containing polymer, or other components. The content of the glycidyl group-containing polymer in the inner layer 21 may be more than 50% in volume ratio. Similarly, the content of the polyacetal resin in the outer layer 22 and the content of the lubricant in the innermost layer are respectively The volume ratio may be more than 50%.

  In addition, at the boundary between the inner layer 21 and the outer layer 22 and at the boundary between the inner layer 21 and the innermost layer, the constituent material may change continuously via the interface, but preferably the constituent material changes discontinuously. It is supposed to be. With such a structure, the interface between the inner layer 21 and the outer layer 22 and the boundary between the inner layer 21 and the innermost layer each become a slip surface, and the fluidity of the composition for injection molding is particularly improved. As a result, the moldability during injection molding is particularly high, and finally a sintered body with high dimensional accuracy is obtained.

(Inorganic powder)
Here, the inorganic powder used in the present invention will be described in detail.
As described above, as the inorganic powder, a powder composed of at least one of a metal material and a ceramic material is used. Specifically, in addition to metal powder and ceramic powder, powder of composite material of metal material and ceramic material, mixed powder of metal powder and ceramic powder, and the like can be mentioned.

Among these, as metal materials, for example, Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Pd, Ag, In, Sn, Sn, Examples thereof include Ta, W, alloys of these metal elements, alloys with other metal elements, and the like, and one or a mixture of two or more of these is used.
Among these, various types such as stainless steel, die steel, high speed tool steel, low carbon steel, Fe—Ni alloy, Fe—Si alloy, Fe—Co alloy, Fe—Ni—Co alloy, etc. Fe-based alloys, Al-based alloys, Ti-based alloys and the like are preferably used. Since such a metal material is excellent in mechanical properties, a sintered body excellent in mechanical properties and applicable to a wide range of uses can be obtained.

Examples of the stainless steel include SUS304, SUS316, SUS317, SUS329, SUS410, SUS430, SUS440, and SUS630.
Examples of the Al-based alloy include aluminum simple substance and duralumin.

  Examples of the Ti-based alloy include titanium alone or an alloy of titanium and a metal element such as aluminum, vanadium, niobium, zirconium, tantalum, and molybdenum. Specifically, Ti-6Al-4V, Ti-6Al-7Nb etc. are mentioned. The Ti-based alloy may contain non-metallic elements such as boron, carbon, nitrogen, oxygen and silicon in addition to these metal elements.

Such a metal powder may be produced by any method. For example, an atomization method (water atomization method, gas atomization method, high-speed rotating water atomization method, etc.), reduction method, carbonyl method, pulverization method, etc. What was manufactured by the method can be used.
Among these, it is preferable to use what was manufactured by the atomizing method for metal powder. According to the atomizing method, a metal powder having an extremely small average particle diameter as described above can be efficiently produced. Moreover, there can be obtained a metal powder having a small particle size variation and a uniform particle size. Therefore, by using such a metal powder, the formation of pores in the sintered body can be surely prevented, and the density can be improved.
In addition, since the metal powder produced by the atomizing method has a spherical shape that is relatively close to a true sphere, the metal powder has excellent dispersibility and fluidity with respect to the binder. For this reason, when the granulated powder is filled into a mold and molded, the filling property can be improved, and a denser sintered body can be finally obtained.

  On the other hand, examples of the ceramic material include alumina, magnesia, beryllia, zirconia, yttria, forsterite, steatite, wollastonite, mullite, cordierite, oxide-based ceramic materials such as ferrite, sialon, cerium oxide, and silicon nitride. Non-oxide ceramic materials such as aluminum nitride, boron nitride, titanium nitride, silicon carbide, boron carbide, titanium carbide, tungsten carbide, etc., and one or a mixture of two or more of these are used. .

The average particle size of the inorganic powder used in the present invention is preferably 1 μm to 30 μm, more preferably 3 μm to 20 μm, and even more preferably 3 μm to 10 μm. A metal powder having such a particle size can finally produce a sufficiently dense sintered body while avoiding significant aggregation and a decrease in compressibility during molding.
In addition, when an average particle diameter is less than the said lower limit, an inorganic powder becomes easy to aggregate and there exists a possibility that the compressibility at the time of shaping | molding may fall remarkably. On the other hand, when the average particle diameter exceeds the upper limit, the gap between the powder particles becomes too large, and the final sintered body may not be sufficiently densified.

Further, the average particle diameter is obtained as a particle diameter when the cumulative amount reaches 50% on a volume basis by a laser diffraction method.
Also, if the inorganic powder used in the present invention is constituted by the Fe-based alloy, the tap density is preferably at 3.5 g / cm ³ or more, and more preferably at 3.8 g / cm ³ or more . If the inorganic powder has such a large tap density, the filling property between the particles becomes particularly high at the time of molding. For this reason, a particularly dense sintered body can be finally obtained. In addition, the tap density of inorganic powder can be measured according to the tap density measuring method prescribed | regulated to JISZ2512, for example.

The specific surface area of the inorganic powder used in the present invention is not particularly limited, but is preferably 0.15 m ² / g or more and 0.8 m ² / g or less, and preferably 0.2 m ² / g or more and 0.7 m ^2. / G or less, more preferably 0.3 m ² / g or more and 0.6 m ² / g or less. Thus, if it is an inorganic powder with a large specific surface area, since surface activity (surface energy) will become high, it can sinter easily even if provision of less energy. Therefore, when the molded body is sintered, it can be sintered in a shorter time, and the shape retention is easily improved. On the other hand, when the specific surface area exceeds the upper limit, the contact area between the inorganic powder and the binder becomes unnecessarily wide, and the stability and fluidity of the injection molding composition may be reduced. In addition, the specific surface area of inorganic powder can be measured according to the specific surface area measuring method of the powder (solid) by gas adsorption prescribed | regulated to JISZ8830, for example.
(binder)
Next, the binder used in the present invention will be described in detail.
As described above, the binder used in the present invention contains a polyacetal resin and a glycidyl group-containing polymer having a smaller content.

≪Polyacetal resin≫
The polyacetal resin is a polymer having an oxymethylene structure as a unit structure, and may be a homopolymer containing only formaldehyde as a monomer, a copolymer containing other monomers, or the like. Examples of monomers (comonomer) other than formaldehyde include, for example, oxyalkylene such as oxyethylene and oxypropylene, epichlorohydrin, 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane and the like. In particular, those having an oxyalkylene unit having 2 or more carbon atoms in the molecule are preferably used. The copolymerization amount of the comonomer is not particularly limited, but is preferably 1 mol part or more and 10 mol part or less, more preferably 1 mol part or more and 6 mol part or less with respect to 100 mol parts of the main monomer. Moreover, the arrangement | sequence of the monomer in a copolymer is not specifically limited, Any of random copolymerization, alternating copolymerization, block copolymerization, and graft copolymerization may be sufficient.

Examples of such polyacetal resins include DuPont Delrin, Polyplastics Duracon, Asahi Kasei Kogyo Tenac, Mitsubishi Engineering Plastics Iupital, Quadrant Polypenco Japan Polypen Acetal, Toray Amylas Etc. can be used.
The polyacetal resin preferably has a tensile strength of about 30 MPa to 90 MPa, more preferably about 40 MPa to 80 MPa. A polyacetal-based resin having such tensile strength can particularly improve the shape retention of the molded product after molding.

≪Glycidyl group-containing polymer≫
The glycidyl group-containing polymer is a resin added in a smaller amount than the polyacetal resin, and a polymer containing a glycidyl group such as an epoxy group is used, and a polymer containing an unsaturated glycidyl group is preferably used. It is done. The unsaturated glycidyl group-containing polymer is a polymer containing an unsaturated glycidyl group-containing monomer as a unit structure. Examples of the unsaturated glycidyl group-containing monomer include glycidyl (meth) acrylate, allyl glycidyl ether, α-ethyl glycidyl. Ether, crotonyl glycidyl ether, glycidyl crotonate, itaconic acid monoalkyl ester monoglycidyl ester, fumaric acid monoalkyl ester monoglycidyl ester, maleic acid monoalkyl ester monoglycidyl ester, alicyclic epoxy group-containing (meth) acrylate, etc. As the glycidyl group-containing polymer, those containing one or more of these unit structures are used. In particular, glycidyl (meth) acrylate is preferably used. The glycidyl group contained in the glycidyl group-containing polymer is ring-opened during kneading, molding or the like, and bonded to the hydroxyl group on the particle surface of the inorganic powder. As a result, the inorganic powder and the glycidyl group-containing polymer exhibit high adhesion. As a result, the inner layer 21 is stably formed.

  The unsaturated glycidyl group-containing polymer is preferably a copolymer containing the unsaturated glycidyl group-containing monomer as described above and an ethylenically unsaturated ester compound monomer. A copolymer containing an ethylenically unsaturated ester compound monomer as a unit structure contributes to the realization of an injection molding composition that can be molded with high shape retention. In particular, the ethylenically unsaturated ester compound monomer and the unsaturated glycidyl group-containing monomer contribute to the affinity with the particles of the inorganic powder. Therefore, the glycidyl group-containing polymer separates the particles of the inorganic powder and the polyacetal resin. It will function reliably as a partition wall. Finally, it is possible to manufacture a high-quality sintered body with particularly few deformations and defects.

Examples of the ethylenically unsaturated ester compound monomer include vinyl acetate, vinyl propionate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, and carboxylic acid vinyl esters such as butyl methacrylate, Examples include α, β-unsaturated carboxylic acid alkyl esters, and those containing one or more of these are used.
Among these ethylenically unsaturated ester compound monomers, those containing at least one of vinyl acetate and methyl acrylate are particularly preferably used.

  The unsaturated glycidyl group-containing polymer preferably contains a nonpolar α-olefin monomer in addition to the unsaturated glycidyl group-containing monomer as described above. By including a non-polar α-olefin monomer as a unit structure, the glycidyl group-containing polymer is rich in affinity with the polyacetal resin. As a result, the glycidyl group-containing polymer not only has an affinity for the particles of the inorganic powder as described above, but also has an affinity for the polyacetal resin. It can exist stably with the polyacetal resin. As a result, it is possible to particularly suppress a decrease in shape retention of the molded body.

Examples of the nonpolar α-olefin monomer include ethylene, propylene, butene-1, hexene-1, octene-1, 4-methylpentene-1, and among them, ethylene, propylene, butene-1, Hexene-1 and octene-1 are preferred.
Since the inner layer 21 mainly composed of a glycidyl group-containing polymer is on the particle 2 side, the outer layer 22 needs to have a resistance to the catalytic action described above, while the outer layer 22 has a higher melting point and higher rigidity than the inner layer 21. It must have excellent degradability despite being expensive. By using a polyacetal-based resin and using an unsaturated glycidyl group-containing polymer, a kneaded product 1 satisfying all these needs can be obtained.

Moreover, since the unsaturated glycidyl group-containing polymer has both excellent shielding properties against catalytic action by metal elements and compatibility with the polyacetal resin, the moldability can be further improved. Accordingly, both shape retention and formability can be achieved.
The content of the glycidyl group-containing polymer in the composition for injection molding is preferably 1% by mass or more and 30% by mass or less, and preferably 2% by mass or more and 20% by mass or less with respect to the content of the polyacetal resin. Is more preferable. By keeping the content of the glycidyl group-containing polymer within the above range, both shape retention and moldability can be achieved at a higher level.

The melting point of the glycidyl group-containing polymer is preferably 65 ° C. or higher and 105 ° C. or lower, and more preferably 70 ° C. or higher and 100 ° C. or lower. Thereby, when the composition for injection molding is kneaded or molded, the glycidyl group-containing polymer can be reliably melted and the inner layer 21 can be formed.
Furthermore, the difference between the melting point of the glycidyl group-containing polymer and the melting point of the polyacetal resin is preferably 55 ° C. or higher and 120 ° C. or lower, and more preferably 60 ° C. or higher and 115 ° C. or lower. If the difference in melting point between the glycidyl group-containing polymer and the polyacetal-based resin is within the above range, shape retention and moldability can be further enhanced.

In the glycidyl group-containing polymer, the unit structure constituting the unsaturated glycidyl group-containing polymer includes, as described above, an unsaturated glycidyl group-containing monomer, and if necessary, an ethylenically unsaturated ester compound monomer. And non-polar α-olefin monomers are used.
These abundance ratios are not particularly limited, but as an example, the nonpolar α-olefin monomer is preferably 300 parts by mass or more and 2000 parts by mass or less, based on 100 parts by mass of the unsaturated glycidyl group-containing monomer, and 400 parts by mass The amount is more preferably 1500 parts by mass or less. Thereby, the compatibility with the polyacetal resin by the nonpolar α-olefin monomer and the affinity with the particle 2 by the unsaturated glycidyl group-containing monomer can be balanced to a high degree, and the shape retention and moldability can be improved. Both can be particularly enhanced.

In addition, the ethylenically unsaturated ester compound monomer is preferably 20 parts by weight or more and 80 parts by weight or less, more preferably 25 parts by weight or more and 75 parts by weight or less with respect to 100 parts by weight of the unsaturated glycidyl group-containing monomer. .
The melt flow rate of the glycidyl group-containing polymer is preferably about 0.5 g / 10 min to 50 g / 10 min, more preferably about 3 g / 10 min to 40 g / 10 min. If the melt flow rate is within the above range, the inner layer 21 is reliably formed, and the shape retention of the injection molding composition is particularly improved. The melt flow rate can be measured at a measurement temperature of 190 ° C. and a measurement load of 2.16 kg according to the method defined in JIS K 6922-2.

Furthermore, the glycidyl group-containing polymer preferably has a tensile strength of about 4 MPa to 25 MPa, more preferably about 5 MPa to 20 MPa. Thereby, the glycidyl group-containing polymer becomes rich in fluidity even when melted, and the inner layer 21 can be more reliably formed.
The weight average molecular weight of the glycidyl group-containing polymer is appropriately set in consideration of the melt flow rate as described above, but as an example, it is preferably 10,000 or more and 400,000 or less, preferably 30,000 or more and 300,000 or less. It is more preferable that

≪Lubricant≫
The binder used in the present invention may contain a lubricant in addition to the polyacetal resin and the glycidyl group-containing polymer. By adding a lubricant to the composition for injection molding, the lubricant is melted first at the time of kneading, so that the uniformity at the time of kneading is improved. This is because the polyacetal resin, which is the main material of the binder, is often a resin material that has low compatibility with other binder components and inorganic powders, and compatibility is imparted by the presence of a lubricant. Because. As a result, even if the shape of the particles of the inorganic powder is distorted, the inorganic powder and the binder are uniformly mixed, and as described above, the glycidyl group-containing polymer is surely placed between the particles of the inorganic powder and the polyacetal resin. To penetrate. Moreover, since the fluidity | liquidity of the composition for injection molding improves, shape transfer property and mold release property improve, and the uniformity of a molded object also improves. As a result, the moldability of the molded body is improved.

Examples of the lubricant include waxes, higher fatty acids, alcohols, fatty acid metals, nonionic surfactants, silicone-based lubricants, etc., and one or a mixture of two or more thereof is used.
Among these, as waxes, for example, plant wax such as candelilla wax, carnauba wax, rice wax, wax, jojoba oil, animal wax such as beeswax, lanolin, spermaceti, montan wax, ozokerite, Mineral wax such as ceresin, paraffin wax, microcrystalline wax, natural wax such as petroleum wax such as petrolatum, synthetic hydrocarbons such as polyethylene wax, montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives Modified wax, hydrogenated wax such as hydrogenated castor oil, hydrogenated castor oil derivative, fatty acid such as 12-hydroxystearic acid, acid amide such as stearamide, esthetic such as phthalimide anhydride Synthetic waxes can be mentioned the like, may be used singly or in combination of two or more of them.

Examples of higher fatty acids include stearic acid, oleic acid, linoleic acid and the like, and saturated fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid are particularly preferably used.
Examples of alcohols include polyhydric alcohols, polyglycols, polyglycerols, and the like, and cetyl alcohol, stearyl alcohol, oleyl alcohol, mannitol, and the like are particularly preferably used.

  Examples of the fatty acid metal include lauric acid, stearic acid, succinic acid, stearyl lactic acid, lactic acid, phthalic acid, benzoic acid, hydroxystearic acid, ricinoleic acid, naphthenic acid, oleic acid, palmitic acid, and erucic acid. Examples include compounds of higher fatty acids and metals such as Li, Na, Mg, Ca, Sr, Ba, Zn, Cd, Al, Sn, Pb, and Cd. In particular, magnesium stearate, calcium stearate, sodium stearate Zinc stearate, calcium oleate, zinc oleate, magnesium oleate and the like are preferably used.

Moreover, as a nonionic surfactant type | system | group lubricant, electro stripper TS-2, electro stripper TS-3 (Kao) etc. are mentioned, for example.
Examples of the silicone-based lubricant include dimethylpolysiloxane and modified products thereof, carboxyl-modified silicone, α-methylstyrene-modified silicone, α-olefin-modified silicone, polyether-modified silicone, fluorine-modified silicone, hydrophilic specially-modified silicone, and olefin polysiloxane. Examples include ether-modified silicone, epoxy-modified silicone, amino-modified silicone, amide-modified silicone, and alcohol-modified silicone.

  Among these lubricants, it is particularly preferable to contain at least one of waxes and saturated fatty acids. By including waxes, the composition for injection molding has higher uniformity during kneading. As a result, the inorganic powder and the binder are mixed more uniformly. Moreover, since the fluidity | liquidity of the composition for injection molding improves more, a moldability will also improve further. Moreover, since a saturated fatty acid contains a long-chain alkyl group and does not contain an unsaturated bond, it can act as an excellent lubricant and can improve the moldability of the composition for injection molding.

  As the waxes, petroleum waxes or modified products thereof are particularly preferably used, paraffin wax, microcrystalline wax, carnauba wax or derivatives thereof are more preferably used, and paraffin wax or carnauba wax is more preferably used. Since these waxes are excellent in compatibility with the polyacetal resin, it is possible to prepare a homogeneous binder.

The weight average molecular weight of the wax is preferably 100 or more and less than 10,000, and more preferably 200 or more and 5000 or less. By setting the weight average molecular weight of the wax within the above range, the inorganic powder and the binder can be more uniformly mixed, and the moldability of the injection molding composition can be further improved.
Moreover, it is preferable that carbon number of a saturated fatty acid is about 12 or more and 20 or less. Thereby, a moldability can be improved especially.

Further, the content of the lubricant in the binder is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 15% by mass or less. By setting the content of the lubricant within the above range, the fluidity of the composition for injection molding can be particularly enhanced.
Further, the ratio of the lubricant to the glycidyl group-containing polymer is preferably 0.01 or more and 0.8 or less, and more preferably 0.02 or more and 0.6 or less. By setting the ratio of the lubricant with respect to the glycidyl group-containing polymer within the above range, the balance between the glycidyl group-containing polymer and the lubricant is optimized, and the moldability can be improved without impairing the shape retention during degreasing. Can be increased.

In addition, since the lubricant has a lower melting point than the glycidyl group-containing polymer, the lubricant melts when molded at the above temperature, further improving the permeability of the glycidyl group-containing polymer and improving the fluidity of the polyacetal resin. Enhanced. As a result, shape retention and moldability can be achieved at a higher level.
The melting point of the lubricant is preferably lower than the melting point of the polyacetal resin or the glycidyl group-containing polymer, and the difference between the melting point of the lubricant and the melting point of the glycidyl group-containing polymer is 3 ° C. or more and 70 ° C. or less. Preferably, it is 5 ° C. or more and 50 ° C. or less. If the difference in melting point between the lubricant and the glycidyl group-containing polymer is within the above range, both shape retention and moldability can be achieved at a higher level.

Further, as the lubricant, those having a melting point of 30 ° C. or higher and 100 ° C. or lower are preferably used, and those having a melting point of 50 ° C. or higher and 95 ° C. or lower are more preferably used.
Moreover, when waxes are included as the lubricant, it is preferable to include a plurality of types of waxes having different melting points. Thereby, the moldability of the composition for injection molding can be improved. In this case, the difference in melting point between the waxes having the highest melting point and the waxes having the lowest melting point is not particularly limited, but is preferably about 3 ° C to 40 ° C, and preferably about 5 ° C to 30 ° C. Is more preferable. Specific examples include paraffin wax and carnauba wax.

≪Other ingredients≫
Moreover, the binder used for this invention may contain the other component.
Other components include, for example, fatty acid esters such as palm oil, diethyl phthalate, phthalic acid esters such as dibutyl phthalate, adipic acid esters such as dibutyl adipate, sebacic acid esters such as dibutyl sebacate, Examples include polyvinyl alcohol, polyvinyl pyrrolidone, polyether, polypropylene carbonate, ethylene bisstearamide, sodium alginate, agar, gum arabic, resin, sucrose, ethylene-vinyl acetate copolymer (EVA), etc. Species or a combination of two or more can be used.

The content of such other components in the binder is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 8% by mass or less.
Further, the ratio of other components to the glycidyl group-containing polymer is preferably 0.005 or more and 0.3 or less, and more preferably 0.01 or more and 0.2 or less.
Furthermore, as other components, for example, polyolefins such as polyethylene, polypropylene, polybutylene and polypentene, polyolefin-based copolymers such as polyethylene-polypropylene copolymer, polyethylene-polybutylene copolymer, and hydrocarbons such as polystyrene. Resin.

The injection molding composition may contain an antioxidant, a degreasing accelerator, a surfactant and the like in addition to the above components.
Further, the content of the binder in the composition for injection molding is appropriately set according to the metal powder and the ceramic powder, but it is about 1 to 50 parts by mass with respect to 100 parts by mass of the inorganic powder. Preferably, it is more preferably about 3 parts by mass or more and 30 parts by mass or less. Thereby, the composition for injection molding becomes a thing excellent in the shape retention property at the time of degreasing especially.
Using the inorganic powder and binder as described above, the kneaded product 1 (the composition for injection molding of the present invention) is obtained through the above-described steps.
The obtained kneaded material 1 becomes a sintered body through a molding process, a degreasing process, and a firing process described later. Hereinafter, each step will be described.

(Molding process)
The resulting kneaded product is molded. Thereby, the molded object of a desired shape and a dimension is manufactured.
An injection molding method is used as the molding method. Prior to injection molding, the injection molding composition may be pelletized as necessary. The pelletizing process is a process of pulverizing the compound using a pulverizer such as a pelletizer. The pellets thus obtained have an average particle size of about 1 mm to 10 mm.

Next, the obtained pellets are put into an injection molding machine and injected into a mold to be molded. Thereby, the molded object to which the shape of the mold was transferred is obtained.
It should be noted that the shape and size of the molded body to be manufactured is determined in consideration of the shrinkage due to subsequent degreasing and sintering.
Moreover, you may make it give post-processing, such as machining and laser processing, to the obtained molded object as needed.
The material temperature is degree 80 ° C. or higher 210 ° C. or less in the molding process, the injection pressure is preferably 500MPa or less (0.5 t / cm ² or more 5t / cm ² or less) less than approximately 50 MPa.

(Degreasing process)
Next, degreasing treatment is performed on the obtained molded body. Thereby, the binder contained in a molded object is removed (degreasing), and a degreased body is obtained.
In addition, the lubricant is often decomposed before the polyacetal-based resin or the glycidyl group-containing polymer at the time of degreasing or molding before that, and is often released to the outside. It is formed. In the degreasing step, a decomposition product of the polyacetal resin or the glycidyl group-containing polymer is easily released through this flow path, and therefore, the degreasing treatment can be performed while preventing cracks and the like from occurring in the molded body. . As a result, the shape retention of the molded body (defatted body) can be particularly enhanced.

This degreasing treatment is not particularly limited, but in an oxidizing atmosphere such as oxygen or nitric acid gas or in a non-oxidizing atmosphere, for example, under vacuum or reduced pressure (for example, 1.33 × 10 ⁻⁴ Pa to 13.3 Pa). Alternatively, the heat treatment is performed in a gas such as nitrogen gas or argon gas.
The treatment temperature in the degreasing step (heat treatment) is not particularly limited, but is preferably 100 ° C. or higher and 750 ° C. or lower, and more preferably 150 ° C. or higher and 700 ° C. or lower.

The treatment time (heat treatment time) in the degreasing step (heat treatment) is preferably 0.5 hours or more and 20 hours or less, and more preferably 1 hour or more and 10 hours or less.
Further, degreasing by such heat treatment may be performed in a plurality of steps (stages) for various purposes (for example, for shortening the degreasing time). In this case, for example, a method in which the first half is degreased at a low temperature and the second half at a high temperature, a method in which low temperature and high temperature are repeated, and the like can be mentioned.
In addition, after the degreasing treatment as described above, the obtained degreased body may be subjected to various post-processings for the purpose of, for example, deburring or forming a microstructure such as a groove.
In addition, the binder in a molded object does not need to be removed completely by degreasing, for example, the one part may remain | survive when the degreasing process is completed.

(Baking process)
Next, the degreased body that has been subjected to the degreasing treatment is fired. Thereby, a degreased body is sintered and a sintered body is obtained.
The firing conditions are not particularly limited, but in a non-oxidizing atmosphere, for example, in a vacuum or under reduced pressure (for example, 1.33 × 10 ⁻⁴ Pa to 133 Pa), or in an inert gas such as nitrogen gas or argon gas This is done by performing a heat treatment. Thereby, it can prevent that metal powder will oxidize.

Moreover, when a metal material is included in the inorganic powder, when firing, it is preferable to place a degreased body in a container made of the same kind of metal material as the metal material and fire in that state. Thereby, since the metal component in a degreased body becomes difficult to volatilize, it can prevent that the metal composition of the sintered compact finally obtained will change from the target composition.
The container to be used is not a sealed structure, but preferably has a suitable hole or gap. Thereby, the atmosphere inside the container and the outside of the container can be made the same, and the atmosphere inside the container can be prevented from changing to an unintended one. Moreover, it is preferable that there is a sufficient gap between the container and the degreased body without causing as close contact as possible.

Note that the atmosphere in which the firing process is performed may change during the process. For example, a reduced-pressure atmosphere may be set first, and an inert atmosphere may be switched on the way.
Moreover, you may perform a baking process in 2 steps or more. Thereby, the efficiency of sintering can be improved and firing can be performed in a shorter firing time.
Moreover, it is preferable to perform a baking process continuously with the above-mentioned degreasing process. Thereby, a degreasing process can serve as a pre-sintering process, can preheat a degreased body, and can sinter a degreased body more certainly.

The firing temperature is appropriately set according to the kind of the inorganic powder. In the case of a metal powder, the firing temperature is preferably 1000 ° C. or higher and 1650 ° C. or lower, more preferably 1050 ° C. or higher and 1500 ° C. or lower. In the case of ceramic powder, it is preferably 1250 ° C. or higher and 1900 ° C. or lower, more preferably 1300 ° C. or higher and 1800 ° C. or lower.
The firing time is preferably 0.5 hours or more and 20 hours or less, more preferably 1 hour or more and 15 hours or less.

Moreover, such a baking process may be performed in a plurality of steps (stages) for various purposes (for example, for the purpose of shortening the baking time, etc.). In this case, for example, a method in which the first half is fired at a low temperature and the second half is fired at a high temperature, a method in which a low temperature and a high temperature are repeated, and the like can be mentioned.
Further, after the firing step as described above, the obtained sintered body is subjected to machining, electric discharge machining, laser machining, etching, etc. for the purpose of deburring, forming a microstructure such as a groove, etc. You may give it.

Note that the obtained sintered body may be subjected to HIP processing (hot isostatic pressing) or the like, if necessary. Thereby, further densification of a sintered compact can be achieved.
As conditions for the HIP treatment, for example, the temperature is 850 ° C. or higher and 1100 ° C. or lower and the time is 1 hour or longer and 10 hours or shorter.
Further, the pressurizing pressure is preferably 50 MPa or more, and more preferably 100 MPa or more.
The sintered body obtained as described above may be used for any purpose. Examples of its use include various structural parts and various medical structures.

The relative density of the obtained sintered body is expected to be, for example, 95% or more, preferably 96% or more. Such a sintered body has a high sintered density and an excellent appearance and dimensional accuracy.
Further, the tensile strength of the sintered body is expected to be 900 MPa or more when, for example, metal powder is used. Furthermore, the 0.2% yield strength of the sintered body is expected to be 750 MPa or more, for example, when metal powder is used.
As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to these.

Next, specific examples of the present invention will be described.
1. Production of sintered body (Example 1)
First, SUS316L powder (powder No. 1) manufactured by the water atomization method was prepared. About SUS316L powder, the average particle diameter was measured with the particle size distribution measuring apparatus of the laser diffraction system (Microtrac, Nikkiso Co., Ltd. make, HRA9320-X100). The measured values are shown in Table 1.

On the other hand, binders having the compositions shown in Table 2 were prepared, and the first resin, the second resin, and the like (including a lubricant and other components) were freeze-ground. Thus, a first powder obtained by freeze-pulverizing the first resin and a second powder obtained by freeze-pulverizing the second resin and the like were produced.
Specifically, the first resin was put in a pulverization container, and the first resin was pulverized while being cooled with liquid nitrogen. The average particle diameter of the obtained first powder was 53 μm. The average particle size of the second powder was 242 μm.

Next, the SUS316L powder, the first powder, and the second powder were mixed with a V-type mixer and kneaded with a pressure kneader (kneader) at a kneading temperature of 160 ° C. for 30 minutes. This kneading was performed in a nitrogen atmosphere. The mixing ratio of SUS316L powder and binder is shown in Table 1.
Next, the obtained kneaded material was pulverized by a pelletizer to obtain pellets having an average particle diameter of 5 mm.

Next, the obtained pellets were molded by an injection molding machine under molding conditions of material temperature: 190 ° C. and injection pressure: 10.8 MPa (110 kgf / cm ² ). This obtained the molded object. In addition, the shape of a molded object is a cylindrical shape of diameter 0.5mm x height 0.5mm.
Next, the molded body was subjected to a degreasing process under a degreasing condition of temperature: 500 ° C., time: 1 hour, atmosphere: nitrogen gas (atmospheric pressure). This obtained the defatted body.
Next, the degreased body was subjected to a firing treatment under firing conditions of temperature: 1270 ° C., time: 3 hours, atmosphere: nitrogen gas (atmospheric pressure). This obtained the sintered compact.

(Examples 2 to 19)
Sintered bodies were obtained in the same manner as in Example 1 except that the binder having the composition shown in Table 2 was used.
In Example 15, the kneading temperature was 155 ° C. The average particle size of the first powder in these examples was about 40 μm or more and 70 μm or less, and the average particle size of the second powder was about 180 μm or more and 300 μm or less.
In Example 10, a mixture of Tenac HC750 and stearyl alcohol was used as the first resin, and a mixture of E-GA and paraffin wax was used as the second resin.

(Comparative Examples 1-6)
As an inorganic powder, powder No. A sintered body was obtained in the same manner as in Example 1 except that No. 1 was used and the binder having the composition shown in Table 3 was used.
In addition, the 1st resin and 2nd resin in Table 2, 3 and Tables 4-6 mentioned later are shown below.

<First resin>
Tenac HC750: polyacetal copolymer Tenac 7520: polyacetal copolymer Tenac 7054: polyacetal homopolymer <second resin>
E-GMA-VA: glycidyl methacrylate structure 12% by mass, vinyl acetate structure 5% by mass, ethylene structure remainder E-GMA-MA: glycidyl methacrylate structure 3% by mass, methyl acrylate structure 27% by mass, ethylene structure remainder E-GMA: Glycidyl methacrylate structure 12% by mass, ethylene structure remainder E-GA: Glycidyl acrylate structure 12% by mass, ethylene structure remainder The E-GMA-VA has a melt flow rate of 7 g / 10. Min, E-GMA-MA was 7 g / 10 min and E-GMA was 3 g / 10 min.

(Comparative Examples 7 and 8)
Sintered bodies were obtained in the same manner as in Examples 10 and 4 except that the first powder and the second powder of the binder were each pulverized without cooling. The average particle size of the first powder was 50 μm or more and 55 μm or less, and the average particle size of the second powder was 240 μm or more and 255 μm or less.

(Examples 20 to 22)
First, 2% Ni—Fe alloy powder (powder No. 2) produced by the water atomization method was prepared, and the average particle size was measured with a laser diffraction type particle size distribution measuring device. The measured values are shown in Table 1. The composition of the 2% Ni—Fe alloy is as follows: C: 0.4 mass% or more and 0.6 mass% or less, Si: 0.35 mass% or less, Mn: 0.8 mass% or less, P: 0.03 Mass% or less, S: 0.045 mass% or less, Ni: 1.5 mass% or more and 2.5 mass% or less, Cr: 0.2 mass% or less, and Fe: balance.

  Then, sintered bodies were obtained in the same manner as in Example 1 except that the binder having the composition shown in Table 4 was used. The molding conditions were material temperature: 190 ° C. The degreasing conditions were temperature: 600 ° C., time: 1 hour, atmosphere: nitrogen gas (atmospheric pressure). The firing conditions were temperature: 1150 ° C., time: 3 hours, and atmosphere: nitrogen gas (atmospheric pressure).

(Comparative Examples 9-12)
As an inorganic powder, powder No. Sintered bodies were obtained in the same manner as in Example 1 except that the binder having the composition shown in Table 4 was used as the binder.
(Comparative Example 13)
A sintered body was obtained in the same manner as in Example 20 except that the first powder and the second powder of the binder were pulverized without cooling.

(Examples 23 to 25)
First, Ti alloy powder (powder No. 3) produced by the gas atomization method was prepared, and the average particle size was measured by a laser diffraction type particle size distribution measuring device. The measured values are shown in Table 1.
Then, sintered bodies were obtained in the same manner as in Example 1 except that the binder having the composition shown in Table 5 was used. The molding conditions were material temperature: 190 ° C. The degreasing conditions were temperature: 450 ° C., time: 1 hour, atmosphere: nitrogen gas (atmospheric pressure). The firing conditions were temperature: 1100 ° C., time: 3 hours, atmosphere: argon gas (reduced pressure, 1.3 kPa).

(Comparative Examples 14-17)
As an inorganic powder, powder No. A sintered body was obtained in the same manner as in Example 1 except that No. 3 was used and the binder having the composition shown in Table 5 was used.
(Comparative Example 18)
A sintered body was obtained in the same manner as in Example 23 except that the first powder and the second powder of the binder were used without being cooled.

(Examples 26 to 28)
First, alumina powder (powder No. 4) was prepared, and the average particle size was measured with a laser diffraction particle size distribution analyzer. The measured values are shown in Table 1.
Then, sintered bodies were obtained in the same manner as in Example 1 except that the binder having the composition shown in Table 6 was used. The degreasing conditions were temperature: 500 ° C., time: 2 hours, and atmosphere: nitrogen gas (atmospheric pressure). The firing conditions were temperature: 1600 ° C., time: 3 hours, and atmosphere: air.

(Comparative Examples 19-22)
As an inorganic powder, powder No. A sintered body was obtained in the same manner as in Example 1 except that No. 4 was used and the binder shown in Table 6 was used.
(Comparative Example 23)
A sintered body was obtained in the same manner as in Example 26 except that the first powder and the second powder of the binder were pulverized without cooling.

2. 2. Evaluation of Kneaded Product 2.1 Evaluation of Viscosity The kneaded product obtained in each Example and each Comparative Example was kept at a temperature of 190 ° C., and the viscosity was measured by a capillograph. The measurement results are shown in Tables 2-6.
2.2 Evaluation of Formaldehyde Generation Amount The amount of formaldehyde generated from the kneaded material during the kneading process was measured for the kneaded materials obtained in each Example and each Comparative Example. The measurement results are shown in Tables 2 and 3. Formaldehyde is generated along with the decomposition of the polyacetal resin, so it can be used as an indicator of the decomposition amount of the polyacetal resin that has been inadvertently decomposed during kneading by measuring the amount of generation. it can. The amount of formaldehyde generated was the formaldehyde concentration measured 10 minutes after the start of kneading.

2.3 Evaluation by Microscopic Observation The kneaded materials obtained in each Example and each Comparative Example were placed under fuming nitric acid at 120 ° C. for 3 hours. Thereby, the polyacetal resin was selectively removed from the kneaded product. Since the polyacetal-based resin decomposes at a temperature lower than the softening point under fuming nitric acid, it can be selectively removed. Therefore, by performing this treatment, the outer layer 22 can be selectively removed from the kneaded product. . As a result, the inorganic powder and the inner layer 21 mainly remain in the kneaded product.

Here, the kneaded material which gave this fuming nitric acid process was observed with the scanning electron microscope. In FIG. 3, the observed image of the kneaded material obtained in Example 4 and Comparative Example 2 is shown as a representative.
Among these, what kneaded nitric acid processing about the kneaded material obtained in Example 4 has a mode that the inner layer 21 exists so that the particle | grains of inorganic powder may be connected as shown to Fig.3 (a). Is recognized. Moreover, it is recognized that the surface of what appears to be particulate is relatively smooth. Therefore, it can be seen that the inorganic powder particles shown in FIG.

  On the other hand, the kneaded product obtained in Comparative Example 2 was subjected to fuming nitric acid treatment, as shown in FIG. 3B, almost the inner layer 21 present so as to connect the particles of the inorganic powder was recognized. Absent. Moreover, it is recognized that the surface of what appears to be in the form of particles has a large difference in shading and relatively low smoothness. Therefore, it is recognized that the inorganic powder particles shown in FIG. 3B have gaps even when the inner layer 21 is present.

In addition, about the thing which gave the fuming nitric acid process about the kneaded material obtained in Example 4, the qualitative analysis was performed with the Fourier transform infrared spectrophotometer (FT-IR). As a result, a spectrum showing characteristics mainly derived from bonds contained in the glycidyl group-containing polymer was obtained.
From the above, it is recognized that the inner layer 21 and the outer layer 22 are reliably formed in each example.

3. Evaluation of Sintered Body 3.1 Evaluation of Sintered Density For the sintered bodies obtained in each Example and each Comparative Example, the density was measured by a method according to the Archimedes method (specified in JIS Z 2501). Further, the relative density of the sintered body was calculated from the measured sintered density and the true density of the metal powder.
3.2 Appearance Evaluation The appearance of 100 sintered bodies obtained in each Example and each Comparative Example was evaluated according to the following evaluation criteria.

<Evaluation criteria for appearance>
A: The number of cracks, defects and deformations is 3 or less.
A: The number of occurrences of cracks, defects and deformations is 4 or more and 10 or less.
Δ: The number of occurrences of cracks, defects and deformations is 11 or more and 50 or less.
X: The number of occurrences of cracks, defects and deformations is 51 or more.

3.3 Evaluation of dimensional accuracy The diameters of 100 sintered bodies obtained in each example and each comparative example were measured with a micrometer. The measured values were evaluated based on the following evaluation criteria based on “normal tolerance of width” defined in JIS B 0411 (normal tolerance of sintered metal product).
<Evaluation criteria for dimensional accuracy>
A: Grade is fine (tolerance ± 0.05 mm or less).
○: The grade is intermediate (tolerance ± 0.05 mm or less ± 0.1 mm or less).
(Triangle | delta): A grade is an average grade (tolerance more than +/- 0.1mm +/- 0.2mm or less).
X: Not acceptable.
2. And 3. The evaluation results are shown in Tables 2-6.

  As is clear from Tables 2 to 6, it was confirmed that the sintered bodies obtained in the respective examples had a higher sintered density than the sintered bodies obtained in the respective comparative examples. Moreover, it was recognized that the sintered bodies obtained in the respective examples were superior in appearance and dimensional accuracy as compared with the sintered bodies obtained in the respective comparative examples. In each example, since the amount of formaldehyde generated from the kneaded material was smaller than in each comparative example, decomposition of the first resin during kneading was effectively suppressed, and as a result, sintering was performed. It is considered that the appearance and dimensional accuracy of the body could be prevented.

4). Evaluation of Evaluation Sample 4.1 Production of Evaluation Sample First, in order to clarify the relationship between the pulverization conditions and the state of the kneaded product, evaluation was performed using binder powder and inorganic powder pulverized under the following pulverization conditions. A kneaded material was prepared as a sample for use. In addition, as an inorganic powder and a binder powder, the same thing as Example 3 was used, and the kneaded material was obtained by knead | mixing on the same conditions as Example 3. FIG.

4.2 Evaluation of Viscosity of Evaluation Sample Next, the prepared evaluation sample was maintained at a temperature of 190 ° C., and the viscosity was measured with a capillograph. And the viscosity was evaluated according to the following evaluation criteria.
<Viscosity evaluation criteria>
○: Viscosity range that can improve both formability and shape retention Δ: Viscosity range where shapeability is high but moldability is slightly inferior ×: Viscosity range where both formability and shape retention are inferior is there

4.3 Evaluation of Viscosity of Evaluation Sample Next, the above-described fuming nitric acid treatment was applied to the prepared evaluation sample, and the outer layer 22 was selectively removed from each evaluation sample.
The remaining portion was observed with a scanning electron microscope to obtain an observation image.
<Evaluation criteria for microscopic images>
○: Many necks are recognized (the necks exist in 70% or more between the particulate matters)
(Triangle | delta): There are few necks (a neck exists in 20% or more and less than 70% between particulate matters)
X: Neck is not recognized (the neck exists in less than 20% between particulate matters)
Table 7 shows the evaluation results of 4.2 and 4.3. In addition, the said neck points out what exists so that a particulate matter may be connected.

As is apparent from Table 7, Samples 1 and 2 using the binder powder obtained by freeze pulverization have a viscosity suitable for shape retention and an inner layer covering the inorganic powder particles is formed. It was recognized that
On the other hand, Sample 3 using a binder powder obtained by room temperature pulverization has low shape retention, and when observed with a microscope, an inner layer covering the particles of the inorganic powder was not observed.
From the above, while using binder powder obtained by pulverization by freeze pulverization and optimizing the rotation speed and average particle size of the pulverizer, it is possible to produce molded products with higher shape retention. It has been observed that compositions can be made.

DESCRIPTION OF SYMBOLS 1 ... Kneaded material 10 ... Composition for injection molding 2 ... Particle 21 ... Inner layer 22 ... Outer layer 3 ... Binder

Claims (9)

A method for producing an injection molding composition comprising an inorganic powder composed of at least one of a metal material and a ceramic material, and a binder containing a polyacetal-based resin and a glycidyl group-containing polymer,
A first pulverization step of freeze-pulverizing the first resin mainly composed of the polyacetal resin;
A second pulverization step of freeze pulverizing the second resin mainly composed of the glycidyl group-containing polymer;
A mixing step of mixing the powder obtained in the first crushing step, the powder obtained in the second crushing step, and the inorganic powder to obtain a mixed powder;
And a kneading step of kneading the mixed powder. A method for producing an injection molding composition.   The melting point of the glycidyl group-containing polymer is lower than that of the polyacetal resin, and the mass content of the glycidyl group-containing polymer in the injection molding composition is less than the mass content of the polyacetal resin. The manufacturing method of the composition for injection molding of description.   The method for producing an injection molding composition according to claim 2, wherein in the kneading step, the mixed powder is kneaded at a temperature between the melting point of the first resin and the melting point of the second resin.   The method for producing an injection molding composition according to any one of claims 1 to 3, wherein the second resin is an unsaturated glycidyl group-containing polymer.   The method for producing an injection molding composition according to claim 4, wherein the unsaturated glycidyl group-containing polymer has a melting point of 65 ° C or higher and 105 ° C or lower.   The method for producing an injection molding composition according to claim 4 or 5, wherein the unsaturated glycidyl group-containing polymer is a copolymer containing an unsaturated glycidyl group-containing monomer and an ethylenically unsaturated ester compound monomer. .   The method for producing an injection molding composition according to claim 4 or 5, wherein the unsaturated glycidyl group-containing polymer is a copolymer containing an unsaturated glycidyl group-containing monomer and a nonpolar α-olefin monomer. .   The method for producing an injection molding composition according to any one of claims 1 to 7, wherein an average particle size of the binder powder is 2 to 50 times that of the inorganic powder.   An inner layer produced by the method for producing an injection molding composition according to any one of claims 1 to 8, provided so as to cover the particles of the inorganic powder and mainly composed of the second resin. And an outer layer located outside the inner layer and mainly composed of the first resin.

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